Method of manufacturing magnetic tunnel junction and magnetic tunnel junction

ABSTRACT

Provided is a method of manufacturing a magnetic tunnel junction that simultaneously realizes removal of oxides on side walls of a magnetic layer and formation of a protective film and prevents deterioration of magnetic characteristics. The method includes: a first step  802  of etching a stacked film including a first magnetic layer, a MgO barrier layer, and a second magnetic layer stacked in order by plasma etching using an oxidizing gas to form the magnetic tunnel junction; and a second step  803  of simultaneously introducing an organic acid gas which is an n-valent acid and a precursor gas having a corresponding metal element valence of m, to form a first protective film on side walls of the magnetic tunnel junction. In the second step, the precursor gas is introduced at a molar ratio of n/m or more with respect to 1 mole of the organic acid gas introduced.

TECHNICAL FIELD

The present invention relates to a method manufacturing of a magnetictunnel junction (MTJ element) and a magnetic tunnel junction.

BACKGROUND ART

In recent years, a magnetoresistive random access memory (MRAM) isexpected to be used as a non-volatile memory that operates with a lowpower consumption and a high speed. A magnetic tunnel junction, which isa basic structure of the magnetoresistive random access memory, has astacked structure in which a barrier layer is sandwiched between a freelayer, which is a magnetic layer whose magnetization direction can bereversed by an external magnetic field or spin transfer, and a fixedlayer, which is a magnetic layer whose magnetization direction is fixed.In the magnetic tunnel junction, the resistance is low when themagnetization directions of the free layer and the fixed layer areparallel, and the resistance is high when the magnetization directionsof the free layer and the fixed layer are antiparallel. A memory inwhich the resistance difference of the magnetic tunnel junctioncorresponds to bit information of “0” and “1” is a magnetoresistiverandom access memory.

As shown in FIG. 1, a cross section of the magnetic tunnel junction hasa stacked structure including a Si substrate 101, an electrode film 102,an underlayer 103 for controlling the crystallinity of a fixed layer andstabilizing the magnetization of the fixed layer, a fixed layer 104 madeof a magnetic material containing elements such as Co and Fe, a MgObarrier layer 105, a free layer 106 made of a magnetic materialcontaining elements such as Co and Fe, a capping layer 107 forprotecting the free layer, a hard mask 108, and a protective film 109.

In the manufacture of the magnetic tunnel junction, it is necessary toutilize a technique of fine etching a stacked film including a magneticlayer containing elements such as Fe and Co used in the free layer 106and the fixed layer 104 and the MgO barrier layer 105 by dry etching. Inorder to prevent deterioration of characteristics of the magnetic tunneljunction due to the moisture or oxygen in the atmosphere, a step offorming a protective film on the magnetic tunnel junction formed by dryetching is also necessary.

Here, the method of fine etching the stacked film by the dry etchingincludes two methods, that is, a method of using ion beam etching and amethod of using plasma etching. In the ion beam etching, a plasmatizedrare gas such as He, Ne, Ar, Kr, or Xe is accelerated by applying a biasthereto and the stacked film is irradiated with the accelerated raregas. Since the chemically inert rare gas is used, it is advantageousthat the gas for treatment does not chemically react with the free layer106, the fixed layer 104, and the MgO barrier layer 105 of the magnetictunnel junction during the ion beam etching. However, when theminiaturization of the MRAM proceeds and the distance between themagnetic tunnel junctions becomes narrow, it can be expected thatelement isolation of the magnetic tunnel junctions is difficult due tothe shadowing effect, and it is difficult to use the magnetic tunneljunction in the future.

In contrast, in the plasma etching, a reactive gas such as hydrogen,nitrogen, or oxygen is plasmatized, the stacked film is irradiated withthe reactive gas, and the etching is realized by the reaction with thestacked film. This technique is directed to high integration as comparedwith the ion beam etching. However, in the case of plasma etching, whenusing plasma produced by using an oxidizing gas or a reducing gas, themagnetic layer used in the fixed layer 104 and the free layer 106 andthe MgO barrier layer are oxidized or reduced by radicals or ionsproduced in the plasma, and thereby the characteristics of the magnetictunnel junction is deteriorated. In particular, in the case of amagnetic tunnel junction that realizes perpendicular magnetization usinginterface magnetic anisotropy at a stack interface between the MgObarrier layer 105 and the fixed layer 104 or the free layer 106,deterioration of magnetic and electrical characteristics due tooxidation or reduction is significant.

Patent Literature 1 discloses a method of plasmatizing CH₃OH gas as amethod of plasma etching using an oxidizing gas. However, due to usingthe oxidizing gas, the fixed layer 104 or the free layer 106 isoxidized, and a magnetic oxide layer 110 that deteriorate the magneticand electrical characteristics of the magnetic tunnel junction is formedon side walls of the magnetic tunnel junction (see FIG. 1).

On the other hand, in a protective film forming step, since a protectivefilm having good coverage can be formed under reduced pressure, achemical vapor deposition (CVD) method using plasma is used. However,since the plasma CVD method generally uses a precursor gas with which areducing gas is mixed, a damaged layer is formed due to a reductionreaction. As a result, the characteristics of the magnetic tunneljunction are deteriorated. In order to avoid the characteristicdeterioration, Patent Literature 2 discloses a method of forming aprotective film having a two-layer structure. In this method, a film isformed by a sputtering method, or the sputtering method and the plasmaCVD method are combined. However, the sputtering method has a problem inthat it is difficult to form a dense film compared to the plasma CVDmethod, and a combination of the sputtering method and the plasma CVDmethod lowers the throughput.

Therefore, in the manufacturing of the magnetic tunnel junction, it isnecessary to remove the magnetic oxide layer 110 formed by plasmaetching and to suppress plasma damage during the formation of theprotective caused by the plasma CVD method.

Patent Literature 3 discloses a method of removing the magnetic oxidelayer 110 formed by plasma etching. After the magnetic layer is etchedby the plasma using an oxidizing gas, a reduction treatment is performedin a radical treatment chamber using the plasma produced by the reducinggas. As a result, the magnetic oxide layer 110 formed during the etchingof the magnetic layer is removed.

Patent Literature 4 discloses a method of recovering the magnetic oxidelayer 110 using an organic acid gas. For example, the magnetic oxidelayer 110 is subjected to a reduction treatment using a formic acid gasor the like. The types of the organic acid gas, such as the formic acidgas, are limited to those reducing the magnetic oxide layer 110 and notreducing the MgO barrier layer 105. With this method, the MgO barrierlayer 105 exhibits good characteristics and the magnetic oxide layer 110can be recovered.

Further, Non-Patent Literature 1 and Non-Patent Literature 2 disclose amethod of using an organic acid gas to remove a damaged layer caused byplasma etching. In this method, the magnetic oxide layer 110 is formedusing plasma of an oxidizing gas after the plasma etching, and then avolatile metal complex is generated by a reaction between the organicacid gas and the magnetic oxide layer 110, thereby removing the damagedlayer.

PRIOR ART LITERATURE Patent Literature

Patent Literature 1: JP-A-2005-042143

Patent Literature 2: JP-A-2010-103303

Patent Literature 3: JP-A-2009-302550

Patent Literature 4: JP-A-2017-123355

Patent Literature 5: JP-A-2013-140891

Non-Patent Literature

Non-Patent Literature 1: J. K.-C. Chen, N. D. Altieri, T. Kim, E. Chen,T. Lill, M. Shen and J. P. Chang, “Directional etch of magnetic andnoble metals. II. Organic chemical vapor etch”, Journal of VacuumScience & Technology A: Vacuum, Surfaces, and Films 35, 05C305 (2017)

Non-Patent Literature 2: J. K.-C. Chen, N. D. Altieri, T. Kim, E. Chen,T. Lill, M. Shen and J. P. Chang, “Ion beam assisted organic chemicalvapor etch of magnetic thin films”, Journal of Vacuum Science &Technology A: Vacuum, Surfaces, and Films 35, 031304 (2017)

SUMMARY OF INVENTION Technical Problem

In the method of recovering the magnetic oxide layer 110 by the reducinggas as disclosed in Patent Literature 3, when the irradiation amount ofhydrogen plasma emitted in the recovery process is too large, the MgObarrier layer 105 is also reduced in addition to the magnetic oxidelayer, so that the electrical characteristics of the magnetic tunneljunction are deteriorated. Therefore, it is necessary to control theirradiation amount of the plasma containing hydrogen to an appropriatevalue. The optimum irradiation amount of the plasma in the recoverymethod of the magnetic oxide layer 110 using the plasma containinghydrogen depends strongly on etching conditions of the magnetic tunneljunction before the recovery method is performed. Therefore, sinceprocess conditions for suppressing the reduction of the MgO barrierlayer 105 and reducing the magnetic oxide layer 110 need to be set inaccordance with the etching conditions in the previous steps, it isdifficult to apply in the mass production process.

On the other hand, the method of suppressing the reduction of the MgObarrier layer 105 and reducing the magnetic oxide layer 110 as disclosedin Patent Literature 4 can reduce the magnetic oxide layer 110 by areaction between the magnetic oxide layer 110 and a reducing gas such asa formic acid. Further, since a condition under which the reactionbetween the MgO barrier layer 105 and formic acid does not proceed canbe realized, the reduction of the MgO barrier layer 105 can besuppressed and the reduction of the magnetic oxide layer 110 can bepromoted.

However, in the reaction disclosed in Patent Literature 4, H₂O isproduced as a reaction product. Since the MgO barrier layer 105 hasdeliquescent property, the MgO barrier layer 105 is deliquesced by H₂O,which may cause short-circuit failure or magnetic propertydeterioration. Therefore, it is required to promote the reduction of themagnetic oxide layer 110 and suppress the deliquescence of the MgObarrier layer 105 caused by H₂O while suppressing the reduction of theMgO barrier layer 105 of the magnetic tunnel junction.

Solution to Problem

An aspect of the invention provides a method of manufacturing a magnetictunnel junction, including: a first step of etching a stacked filmincluding a first magnetic layer, a MgO barrier layer, and a secondmagnetic layer stacked in order by plasma etching using an oxidizing gasto form the magnetic tunnel junction; and a second step ofsimultaneously introducing an organic acid gas which is an n-valent acidand a precursor gas having a corresponding metal element valence of m,to form a first protective film on side walls of the magnetic tunneljunction, in which in the second step, the precursor gas is introducedat a molar ratio of n/m or more with respect to 1 mole of the organicacid gas introduced.

Another aspect of the invention provides a method of manufacturing amagnetic tunnel junction, including: etching a first partial stackedfilm of a stacked film including a first magnetic layer, a barrierlayer, and a second magnetic layer stacked in order, that is a part ofthe stacked film to the second magnetic layer, using a hard mask on thestacked film; simultaneously introducing an organic acid gas which is ann-valent acid and a precursor gas having a corresponding metal elementvalence of m, to remove a surface oxide layer formed on an upper surfaceand side walls of the hard mask and side walls of the first partialstacked film and form, on the upper surface and the side walls of thehard mask and the side walls of the first partial stacked film, a hardcoating having an etching resistance more excellent than that of thehard mask; and etching a second partial stacked film of the stacked filmon and below the barrier layer.

Advantageous Effect

A magnetic oxide layer formed on side walls of a magnetic tunneljunction can be removed and deterioration of characteristics of themagnetic tunnel junction can be suppressed. Further, corner rounding ofa hard mask can be suppressed.

Other problems and novel features will become apparent from thedescription and the attached drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a cross section of a magnetic tunnel junction.

FIG. 2 shows an overall flow of a first embodiment and a secondembodiment.

FIG. 3A is a cross-sectional view of the magnetic tunnel junction in aprocess flow of the first embodiment.

FIG. 3B is a cross-sectional view of the magnetic tunnel junction in theprocess flow of the first embodiment.

FIG. 3C is a cross-sectional view of the magnetic tunnel junction in theprocess flow of the first embodiment.

FIG. 3D is a cross-sectional view of the magnetic tunnel junction in theprocess flow of the first embodiment.

FIG. 3E is a cross-sectional view of the magnetic tunnel junction in theprocess flow of the first embodiment.

FIG. 3F is a cross-sectional view of the magnetic tunnel junction in theprocess flow of the first embodiment.

FIG. 4 shows examples of an organic acid that can be used to reduce amagnetic oxide layer.

FIG. 5 shows volatilization temperatures of volatile metal complexes ofFe and Co.

FIG. 6 shows examples of a precursor gas.

FIG. 7 shows desired molar ratios of the precursor gas to an organicacid gas.

FIG. 8 is a flowchart of a method of manufacturing the magnetic tunneljunction of the first embodiment.

FIG. 9 is a flowchart of a method of manufacturing a magnetic tunneljunction of the second embodiment.

FIG. 10 is a flowchart of a method of manufacturing a magnetic tunneljunction (modification).

FIG. 11 is a flowchart of a method of manufacturing a magnetic tunneljunction (modification).

FIG. 12 is a flowchart of a method of manufacturing a magnetic tunneljunction of a third embodiment.

FIG. 13A is a cross-sectional view of the magnetic tunnel junction in aprocess flow of the third embodiment.

FIG. 13B is a cross-sectional view of the magnetic tunnel junction inthe process flow of the third embodiment.

FIG. 13C is a cross-sectional view of the magnetic tunnel junction inthe process flow of the third embodiment.

FIG. 13D is a cross-sectional view of the magnetic tunnel junction inthe process flow of the third embodiment.

FIG. 13E is a cross-sectional view of the magnetic tunnel junction inthe process flow of the third embodiment.

FIG. 14 is a flowchart of a method of manufacturing the magnetic tunneljunction of the third embodiment.

FIG. 15A is a cross-sectional view of the magnetic tunnel junction inthe process flow of the third embodiment.

FIG. 15B is a cross-sectional view of the magnetic tunnel junction inthe process flow of the third embodiment.

FIG. 15C is a cross-sectional view of the magnetic tunnel junction inthe process flow of the third embodiment.

FIG. 16 is a flowchart of a method of manufacturing a magnetic tunneljunction of a fourth embodiment.

FIG. 17 is a flowchart of a method of manufacturing a magnetic tunneljunction (modification).

DESCRIPTION OF EMBODIMENTS

FIG. 2 shows an overall flow of a first embodiment and a secondembodiment. First, a magnetic oxide layer 110 is formed on side walls ofa magnetic tunnel junction by plasma etching using an oxidizing gas orplasma of an oxidizing gas after plasma etching (step 201). When a freelayer 106 and a fixed layer 104 are magnetic layers containing elementssuch as Fe and Co, the magnetic oxide layer 110 of Fe₂O₃, Fe₃O₄, Co₃O₄,or the like is formed on the side walls. Since the magnetic oxide layer110 has a magnetic property different from that of the magnetic layerssuch as the free layer 106 and the fixed layer 104, the performance ofthe magnetic tunnel junction may be influenced. In addition, themagnetic oxide layer 110 may have conductivity, which is a reason for ashort circuit failure of the magnetic tunnel junction. The magneticoxide layer 110 has a thickness of about several nanometers with respectto several tens of nanometers in diameter of the magnetic tunneljunction.

Subsequently, an organic acid gas and a precursor gas are introducedinto a chamber for etching the magnetic tunnel junction (step 202). As afirst reaction, the organic acid gas (such as a formic acid) reacts withoxides such as Fe₂O₃, Fe₃O₄, and Co₃O₄ to form a volatile metal complexof Fe or Co. When the metal complex of Fe or Co is volatilized, themagnetic oxide layer 110 formed on the side walls of the magnetic tunneljunction is removed. This first reaction produces H₂O at the same time.In step 202, a second reaction is generated in which the precursor gas(Al(acac)₃) reacts with H₂O produced in the first reaction. As a result,a first protective film (such as Al₂O₃) is formed on the side walls ofthe magnetic tunnel junction. The thickness of the first protective filmis about several nanometers that is substantially equal to the thicknessof the magnetic oxide layer 110. As a method of introducing the organicacid gas and the precursor gas in step 202, there are a method ofsimultaneously introducing the organic acid gas and the precursor gasand a method of alternately introducing the organic acid gas and theprecursor gas.

Finally, a second protective film covering the magnetic tunnel junctionis formed. Since this protective film is required to have excellentbarrier property, it is desirable to form the protective film using aninsulating material such as SiN, SiO₂, Al₂O₃, Ta₂O₅, or TiO₂. Asputtering method, a plasma CVD method, or the like can be applied toform the second protective film, and a method capable of forming theprotective film with good coverage under reduced pressure is desirable.

First Embodiment

FIGS. 3A to 3F are cross-sectional views of a magnetic tunnel junctionin a process flow of the first embodiment. In this embodiment, magneticoxide layers 310, which are the oxidation damage on side walls, areremoved, and an insulating oxide is formed as a protective film.

A stacked film for forming the magnetic tunnel junction is formed on alower electrode film 302 on a Si substrate 301. As a stacked film, anunderlayer 303 for controlling the crystallinity of a magnetic materialand stabilizing the magnetization of a fixed layer, a fixed layer 304made of a magnetic material containing elements such as Co or Fe, a MgObarrier layer 305, a free layer 306 made of a magnetic materialcontaining elements such as Co or Fe, a capping layer 307 for protectingthe free layer, and a hard mask 308 are stacked in order. A resist mask309 having a prescribed pattern is formed on the hard mask 308 forelement isolation. FIG. 3A shows this step.

Since the magnetic tunnel junction is formed in a wiring layer of asemiconductor device, although not shown in FIG. 3A, a transistor forselecting each magnetic tunnel junction or a wiring for coupling eachelement is formed between the Si substrate 301 and the lower electrodefilm 302 forming the wiring layer. Here, used as a mask for etching themagnetic tunnel junction, the hard mask 308 is desired to be made of ametal material such as Ta, W, TaN, Ti, TiN, or Ru.

The stacked structure of the magnetic tunnel junction of the presentembodiment is not limited to FIG. 3A, and may have at least the fixedlayer 304 made of a magnetic material, the MgO barrier layer 305, andthe free layer 306 made of a magnetic material, and the stackedstructure thereof is not limited. For example, two or more stackedstructures of the fixed layer 304, the MgO barrier layer 305, and thefree layer 306 may be stacked in order to realize a multi-value magnetictunnel junction. Further, the invention is not limited to a bottom pinstructure as shown in FIG. 3A, and may be a top pin structure in whichthe free layer 306 is formed on a lower layer of the MgO barrier layer305 and the fixed layer 304 is formed on an upper layer of the MgObarrier layer 305.

FIG. 3B shows a step of etching the hard mask 308 using the resist mask309. The etching can be either ion beam etching or plasma etching. Afterthe hard mask 308 is etched, the remaining resist mask 309 is removed.

FIG. 3C shows a step of etching the remaining stacked films (303 to 307)using the hard mask 308. For etching the stacked films (303 to 307),plasma etching using an oxidizing gas, which is suitable for fineetching, is desirable. Since the oxidizing gas is used in the plasmaetching, oxidation proceeds on side walls of the free layer 306 and thefixed layer 304 composed of magnetic layers containing elements such asCo and Fe, and the magnetic oxide layers 310 are formed on the sidewalls. As described with reference to FIG. 1, the magnetic oxide layer310 is an oxide of magnetic substances such as Fe₂O₃, Fe₃O₄, or Co₃O₄,and has a thickness of about several nanometers.

FIG. 3D shows a step of removing the magnetic oxide layers 310 to formfirst protective films 311 on the side walls of the free layer 306 andthe fixed layer 304. In order to implement this step, in the firstembodiment, an organic acid gas and a precursor gas are simultaneouslyintroduced into a chamber for etching the magnetic tunnel junction.There are two reactions in this step.

A reaction between the organic acid gas and the magnetic oxide layer310, which is a first reaction, will be described. In this step, themagnetic element of the magnetic oxide layer 310 produces a metalcomplex and H₂O due to the reaction between the organic acid gas and themagnetic oxide layer 310. The metal complex is volatile, and themagnetic oxide layer 310 is removed by the volatilization of the metalcomplex. At this time, since the reaction of the organic acid gas withthe MgO barrier layer 305 influences the characteristics of the magnetictunnel junction, it is necessary to prevent the organic acid gas fromreacting with the MgO barrier layer 305 while reacting the organic acidwith the magnetic element of the magnetic oxide layer 310.

A case where the magnetic oxide layer 310 is Fe₂O₃ and the organic acidgas is a formic acid (HCOOH) will be described as an example. In thefirst reaction, in order to remove the magnetic oxide layer 310, it isnecessary to spontaneously proceed the reduction reaction between Fe₂O₃and the formic acid.

Fe₂O₃+6HCOOH=2Fe(HCOO)₃+3H₂O   (reaction formula 1)

(Reaction formula 1) is a reduction reaction of Fe₂O₃ and the formicacid, and a metal complex and H₂O are produced. At this time, since theorganic acid gas can also have a reduction reaction with the MgO barrierlayer 305, it is necessary to select an organic acid gas which does notallow the reduction of the MgO barrier layer 305 to spontaneouslyproceed.

The organic acid gases satisfying this condition are shown in FIG. 4. Itis desirable to use gases containing a carboxyl group (formic acid(HCOOH) gas, acetic acid (CH₃COOH) gas, propionic acid (CH₃CH₂COOH) gas,and the like), or gases containing an aldehyde group (formaldehyde(HCHO) gas, acetaldehyde (CH₃CHO) gas, propionaldehyde (C₂H₅CHO) gas andthe like, or acetylacetone (C₅H₈O₂) gas and the like.

The magnetic oxide layer 310 may be Fe₃O₄, Co₃O₄, or the like. In thesecases, from the viewpoint of removal by volatilization, the metalcomplex as the reaction product is preferably a volatile metal complexhaving a low volatilization temperature such as Fe(CO)₅, Fe(acac)₃, orCo(acac)₃, but a volatile metal complex containing a carboxyl group oran aldehyde group may be used. The volatilization temperature of themetal complex is preferably 300° C. or lower. FIG. 5 shows the volatiletemperatures (boiling points) of volatile organics of Fe and Co.

In the step shown in FIG. 3D, a second reaction is generated between H₂Oand the precursor gas. H₂O is the reaction product in the first reactiondescribed above. The first protective films 311 are formed on the sidewall portions of the magnetic tunnel junction from which the magneticoxide layers 310 are removed by the second reaction between H₂O and theprecursor gas. When the precursor gas is aluminum acetylacetoneAl(acac)₃,

3H₂O+2Al(acac)₃=Al₂O₃+6H(acac)   (reaction formula 2)

Al₂O₃ is spontaneously produced according to (reaction formula 2). Asthe first protective film 311, in addition to Al₂O₃, oxides such asTiO₂, SiO₂ or Ta₂O₅ which have high insulation properties and do notexhibit magnetism can also be used. The precursor gases satisfying theseconditions are shown in FIG. 6. It is desirable to use an acetylacetonemetal complex (Al(acac)₃ gas, Ti(acac)₄gas, and the like) or a metalcomplex containing a hydroxyl group (Al(CH₃O)₃ gas, Ti(C₃H₇O)₄ gas, andthe like).

When the organic acid gas and the precursor gas are simultaneouslyintroduced and H₂O produced in the first reaction still remains afterthe second reaction, the deliquescent MgO barrier layer 305 may beinfluenced, and the characteristics of the magnetic tunnel junction maybe deteriorated. Therefore, the molar ratio of the organic acid gas tothe precursor gas introduced in the step shown in FIG. 3D is adjustedsuch that H₂O does not remain after the second reaction.

Regarding the adjustment of the molar ratio, FIG. 7 shows the ratio ofprecursor/organic acid according to the valence of a metal elementcorresponding to the precursor gas, taking a case where the organic acidgas is a monovalent acid as an example. For example, when the formicacid HCOOH which is a monovalent acid is used as the organic acid gasand aluminum acetylacetone Al(acac)₃ is used as the precursor gas, itcan be known from the above (reaction formula 1) and (reaction formula2) that H₂O produced in (reaction formula 1) is completely consumed in(reaction formula 2) if the molar ratio is 2 moles of aluminumacetylacetone to 6 moles of formic acid. That is, if the molar ratio ofaluminum acetylacetone is 1/3 or more with respect to 1 mole of theformic acid, H₂O produced in the first reaction can be removed by thesecond reaction. In general, when the organic acid gas is an n-valentacid and the valence of the metal element corresponding to the precursorgas is m, the precursor gas may have a molar ratio of n/m or more withrespect to 1 mole of the organic acid gas.

FIG. 3E shows a step of forming a second protective film 312 coveringthe magnetic tunnel junction. The second protective film 312 is formedby a plasma CVD method. Since the side walls of the free layer 306 andthe fixed layer 304 are already covered with the first protective films311, it is possible to prevent deterioration of characteristics of themagnetic tunnel junction due to gases such as hydrogen, nitrogen, oroxygen or plasma produced during plasma CVD film formation. It isdesirable to form, as the second protective film 312, a protective filmof an insulation material such as SiN, SiO₂, Al₂O₃, Ta₂O₅, or TiO₂because of excellent barrier properties thereof. The method of formingthe second protective film 312 may be a sputtering method or a CVDmethod. The formation of the first protective film 311 in the step shownin FIG. 3D and the formation of the second protective film 312 shown inFIG. 3E may be performed by the same device or different devices.

Thereafter, an insulating interlayer 313 is formed between the magnetictunnel junctions, the second protective film 312 covering the upper partof the magnetic tunnel junction is removed, and an upper electrode film314 is formed so as to be electrically connected to the hard mask 308.FIG. 3F shows the magnetic tunnel junction subjected to these steps.

The above-described method of manufacturing the magnetic tunnel junctionis summarized in FIG. 8 as a flowchart. First, the hard mask layer isetched (step 801), and the stacked film is etched using the oxidizinggas (step 802). At this time, the magnetic oxide layers 310 are formedon the side walls of the magnetic tunnel junction. Thus, bysimultaneously introducing the organic acid gas and the precursor gas,the magnetic oxide layers 310 on the side walls are removed and thefirst protective films 311 are formed (step 803). Thereafter, in step804 shown in FIG. 8, the second protective film 312 covering themagnetic tunnel junction is formed.

By applying the method of manufacturing a magnetic tunnel junctionaccording to the first embodiment, the magnetic oxide layers 310 on theside walls can be removed and the first protective films 311 can beformed. Accordingly, it is possible to simultaneously realize theremoval of etching damages to the magnetic tunnel junction and damagereduction due to the formation of the protective film. In addition,since H₂O produced in the first reaction is removed in the secondreaction, the risk of deliquescence of the MgO barrier layer can beavoided.

Second Embodiment

In a second embodiment, a case where plasma etching without using anoxidizing gas is applied or ion beam etching is applied when a stackedfilm is processed will be described. When these processes are applied,the magnetic oxide layers 310 are not formed in a step (corresponding tostep 802 in FIG. 8) of etching the stacked film. However, since a densefilm can be formed in a subsequent step of forming a protective film(the second protective film 312), it is desirable to form a film by aplasma CVD method. When the second protective film 312 is formeddirectly on the magnetic tunnel junction by the plasma CVD method, themagnetic oxide layers 310 are formed on the side walls of the free layer306 and the fixed layer 304, and the element characteristics aredeteriorated. Therefore, in the second embodiment, even when the stackedfilm is processed by the plasma etching without using the oxidizing gasor by the ion beam etching, damage to the side walls of the magnetictunnel junction in forming the protective film by the plasma CVD methodis reduced by introducing a post-etching oxidation step.

FIG. 9 shows a process flow of a method of manufacturing the magnetictunnel junction according to the second embodiment. Step 901 is a stepof etching the hard mask layer and is the same as step 801 shown in FIG.8. Step 902 is a step of etching the magnetic tunnel junction by theplasma etching without using the oxidizing gas or by the ion beametching. Since no oxidizing gas is used, in step 902, the magnetic oxidelayers 310 are not formed on the side walls of the magnetic tunneljunction. In the plasma etching without using the oxidizing gas, areactive gas such as hydrogen or nitrogen is used, and in the ion beametching, a rare gas such as He, Ne, Ar, Kr, or Xe or a mixed gas thereofis used. In the case of the plasma etching, reductive damage such as thereduction of MgO may be caused on the side walls of the magnetic tunneljunction due to the etching conditions. In the case of the ion beametching, the reactive gas is not used, and therefore neither oxidationdamage nor the reductive damage occurs.

Subsequently, an oxidation step is introduced after the etching (step903). By introducing this step, the magnetic oxide layers 310 can beformed on the side walls of the magnetic tunnel junction in the samemanner as in the first embodiment. In the oxidation step of step 903,the side walls of the magnetic tunnel junction can be oxidized by meansof irradiating the magnetic tunnel junction with the plasma using theoxidizing gas or irradiating the magnetic tunnel junction only withoxygen radicals produced in the plasma using the oxidizing gas. In thecase where the reductive damage is generated in the MgO barrier layerdue to the plasma etching, the reductive damage can be recovered in theoxidation step in step 903.

Since the magnetic oxide layers 310 are formed by introducing theoxidation step in step 903, the first protective films 311 can be formedby removing the magnetic oxide layers 310 on the side walls bysimultaneously introducing an organic acid gas and a precursor gas inthe same manner as in step 803 in FIG. 8. Step 905 is a step of formingthe second protective film 312 of the magnetic tunnel junction, which isthe same as step 804 in FIG. 8, but is formed by a plasma CVD method.

As described above, in the second embodiment, when the plasma etchingwithout using the oxidizing gas or the ion beam etching is used, thedamage to the side walls of the magnetic tunnel junction and thedeterioration of element characteristics in the step of forming thesecond protective film 312 by the plasma CVD method can be reduced byintroducing the post-etching oxidation step.

Hereinafter, a modification applicable to the process flows of the firstembodiment and the second embodiment will be described. In step 803 inFIG. 8 and step 904 in FIG. 9, the organic acid gas and the precursorgas are simultaneously introduced. When the organic acid gas and theprecursor gas are simultaneously introduced, the organic acid gas mayreact with the precursor gas due to the combination thereof, and themagnetic oxide layers 310 on the side walls of the magnetic tunneljunction may not be removed. Therefore, the combination of the organicacid gas and the precursor gas that can be introduced simultaneously islimited. In the present modification, by alternately introducing theorganic acid gas and the precursor gas, the direct reaction between theorganic acid gas and the precursor gas is prevented. The number of timesof alternately introducing the organic acid gas and precursor gas is oneor more.

FIG. 10 shows a modification of the process flow of the method ofmanufacturing the magnetic tunnel junction. Step 1001 corresponds tostep 802 in FIG. 8 and step 903 in FIG. 9. Step 1002 shows a step ofalternately repeating a step 1 of introducing an organic acid gas and astep 2 of introducing a precursor gas. The number of times ofalternately introducing the organic acid gas and precursor gas is one ormore. Accordingly, the magnetic oxide layers 310 on the side walls ofthe magnetic tunnel junction are removed, and the first protective films311 made of Al₂O₃ and the like are formed on the side walls of themagnetic tunnel junction. In order to prevent the first protective films311 from being formed on the side walls before removing the magneticoxide layers 310, in step 1002, it is desirable to start with step 1 ofintroducing the organic acid gas.

The organic acid gases described in FIG. 4 can be applied as the organicacid gas used in step 1 of introducing the organic acid gas. On theother hand, the condition of the precursor gas used in step 2 ofintroducing the precursor gas is not simultaneously introducing theorganic acid gas and the precursor gas, so the limitation of thecombination of the organic acid gas and the precursor gas is relaxed.The precursor gas may be any precursor gas that reacts with H_(d 2)O toform an insulation film, in addition to the precursor gases shown inFIG. 6. Step 1003 corresponds to step 804 in FIG. 8 and step 905 in FIG.9.

In the present modification, the organic acid gas and the precursor gasare alternately introduced to prevent direct reaction between theorganic acid gas and the precursor gas. As a result, the usablecombination of the organic acid gas and the precursor gas can beincreased.

FIG. 11 shows another modification of the process flow of the method ofmanufacturing the magnetic tunnel junction. Although FIG. 11 shows aheat treatment for improving the insulation property of the firstprotective film 311 in the flow of the first embodiment, the heattreatment can also be applied to the second embodiment and themodifications.

Steps 1101, 1102, and 1103 in FIG. 11 are the same as steps 801, 802,and 803 in FIG. 8. Step 1104 is a heat treatment step. By performing aheat treatment in a temperature range of 150° C. to 300° C. in a vacuum,impurities such as C that may be contained in the first protective films311 can be reduced, and barrier properties and insulation properties ofthe first protective film 311 can be improved. A heat treatment methodapplied in step 1104 may be direct heating of a substrate by a heater.Heating by infrared light or laser light irradiation, or overheating byplasma is also feasible. Step 1105 is a step of forming the secondprotective film 312, which is the same as step 804 in FIG. 8.

In the present modification, by introducing the heat treatment after thefirst protective films 311 are formed, the barrier property and theinsulation property of the first protective films 311 can be improved,and the etching damage to the magnetic tunnel junction caused by asubsequent step such as a film forming step of the second protectivefilm 312 can be reduced.

Third Embodiment

In order to form a magnetic tunnel junction, it is known that in a step(for example, the step shown in FIG. 3C) of etching a stacked film bydry etching, the emitted ions are likely to concentrate on an uppercorner portion of the hard mask 308. Therefore, the etching rate of theperipheral portion of the upper surface of the hard mask 308 tends to behigher than the etching rate at the central portion of the uppersurface. As a result, a cross-sectional shape of the hard mask 308during the etching is subjected to corner rounding of the hard maskwhich means the upper corner portion thereof cannot maintain therectangularity and is rounded and retreats.

As the miniaturization of the magnetic tunnel junction proceeds, whenthe diameter of the magnetic tunnel junction becomes smaller, theinfluence of the corner rounding of the hard mask becomes significant.For example, the diameter of the magnetic tunnel junction is small, thehard mask is subjected to the corner rounding during the etching of thestacked film, the flat portion of the upper surface of the hard mask 308eventually disappears, and the entire upper surface is curved (forexample, spherical shape). In this case, the angle between an ionincident direction and the upper surface of the hard mask 308 is not 90°at any portion of the upper surface. Since the etching rate depends onthe ion incident angle, the etching rate tends to increase with theprogress of the corner rounding, and when the flat portion of the uppersurface of the hard mask is lost, the film thickness of the hard mask israpidly decreased thereafter.

On the other hand, in order to electrically connect the magnetic tunneljunction and the upper electrode film 314 as shown in FIG. 3, the hardmask 308 is exposed by subjecting the protective film 312 and theinsulating interlayer 313 to a planarization process such as chemicalmechanical polishing (CMP). That is, the hard mask 308 is used as a plugfor connecting to the upper electrode film 314. At this time, when thefilm thickness of the hard mask 308 is significantly reduced, theprocess margin of the process of exposing the hard mask 308 may bereduced, and an open defect may occur between the magnetic tunneljunction and the upper electrode film without sufficiently exposing thehard mask, and even the magnetic layer of the magnetic tunnel junctionmay be removed in addition to the hard mask.

Patent Literature 5 discloses a method of suppressing the cornerrounding of a hard mask by ion beam etching by forming a hard coating onside walls of a magnetic tunnel junction. According to this, afterpatterning the hard mask, the hard coatings are formed on an uppersurface and side walls of the hard mask and an upper surface of areference layer of the exposed magnetic tunnel junction by a CVD methodor an atomic layer deposition (ALD) method. Thereafter, the hardcoatings on the upper surface of the hard mask and the upper surface ofthe reference layer are removed by etching, and then ion beam etching ofthe stacked film of the magnetic tunnel junction is performed using thehard mask and a hard layer as masks. When the side walls of the hardmask are covered with the hard coatings, it is possible to suppress thecorner rounding of the hard mask when the stacked structure of themagnetic tunnel junction is etched.

However, since the hard coating on the upper surface of the hard mask isalso removed by etching back the hard coating on the upper surface ofthe reference layer, in the etching step of the stacked film of themagnetic tunnel junction, the corner rounding of the hard mask starts toproceed when the hard coatings protecting the side walls of the hardmask are etched away from the top portion and the side walls of the hardmask are exposed. Thus, in Patent Literature 5, the effect ofsuppressing the corner rounding of the hard mask is limited.

In a third embodiment, an organic acid gas and a precursor gas areintroduced into a chamber for etching a magnetic tunnel junction toselectively form a hard coating on a stacked film above the MgO barrierlayer, thereby suppressing the corner rounding of the hard mask. FIG. 12shows a process flow of a method of manufacturing the magnetic tunneljunction according to the third embodiment. As the magnetic tunneljunction according to the third embodiment, a magnetic tunnel junctionformed by etching a stacked film same as that in the first embodiment isexemplified (FIGS. 13A to 13E). In the following description, the samecontents as those of the first embodiment will not be described.

Step 1201 is a step of patterning the hard mask 308 with the resist mask309. The magnetic tunnel junction at this time is the same as that shownin FIG. 3B in the first embodiment. The material of the hard mask 308 isa metal material such as Ta or W in order to form a hard coating to bedescribed later. Ru or the like can be used as the capping layer 307.

Step 1202 is a step of etching the stacked film until the free layer 306using the hard mask 308 to expose the MgO barrier layer 305. In thisstep, an end point of the etching is controlled based on an etchingtime. In the step of etching the free layer 306, plasma etching using anoxidizing gas is used. Since the oxidizing gas is used in the plasmaetching, as shown in FIG. 13A, the side walls and the upper surface ofthe hard mask 308 and the side walls of the capping layer 307 and thefree layer 306 are oxidized to form a surface oxide layer 1301.

The surface oxide layer 1301 depends on the material of the stackedfilm, and is composed of: a nonmagnetic oxide layer 1302 made of, forexample, Ta₂O₅ on the upper surface and side walls of the hard mask 308;a nonmagnetic oxide layer 1303 made of, for example, RuO₂ on the sidewalls of the capping layer 307; and a magnetic oxide layer 1304 made of,for example, Fe₂O₃, Fe₃O₄, and Co₃O₄ on the side walls of the free layer306. The thickness of the surface oxide layer 1301 is about severalnanometers. In Step 1202, since the thickness of the stacked film (306,307) to be etched is about several nanometers, the hard mask 308processed by the etching of this step is less likely to be subjected tocorner rounding.

Step 1203 is a step of simultaneously introducing the organic acid gasand the precursor gas into the chamber for etching the magnetic tunneljunction. The chamber for performing the process of step 1203 ispreferably the same chamber as in the process of step 1202, but anotherchamber may also be used.

The reaction generated in step 1203 will be described. In step 1203, thesurface oxide layer 1301 is removed, and a chemical reaction for forminga hard coating 1305 shown in FIG. 13B is generated. Specifically, on thesurface oxide layer 1301, two reactions proceed. The two reactions are afirst reaction with the organic acid gas and a second reaction with theprecursor gas.

A metal organic and H₂O are produced by the reaction, which is the firstreaction, between the organic acid gas and the surface oxide layer 1301.The metal organic is volatile, and the surface oxide layer 1301 isremoved by the volatilization of the metal organic. At this time, thereaction between the organic acid gas and the surface oxide layer 1301proceeds, while the reaction of the organic acid gas with the MgObarrier layer 305 needs to be prevented. Non-Patent Literature 1discloses a method of removing an oxide by generating a volatile metalcomplex by a reaction between an organic acid gas such as a formic acidgas and an oxide of a metal material containing elements such as Co orFe. Further, Patent Literature 4 discloses that the reduction of MgO orthe modification of MgO to Mg(OH)₂ are prevented and MgO does not reactwith a formic acid when the pressure in a chamber is set within a rangeof 0.1 Pa to 22000 Pa and the treatment temperature is set within arange of 107° C. to 400° C.

Therefore, under conditions that the organic acid to be applied isformic acid (HCOOH) and the reaction between the formic acid and the MgObarrier layer 305 is prevented (for example, the chamber pressure is 100Pa, the treatment temperature is 200° C.), when the organic acid isreacted with the surface oxide layer 1301, the following reductionreactions proceed as the first reaction in the magnetic tunnel junctionshown in FIG. 13A.

Fe₂O₃+6HCOOH=2Fe(HCOO)₃+3H₂O   (reaction formula 1)

Ta₂O₅+10HCOOH=2Ta(HCOO)₅+5H₂O   (reaction formula 3)

RuO₂+4HCOOH=Ru(HCOO)₄+2H₂O   (reaction formula 4)

(Reaction formula 1), (reaction formula 3) and (reaction formula 4) arereactions between the surface oxide layer 1301 and the organic acid gas(formic acid) and produce metal complexes and H₂O. The reactions of(reaction formula 1), (reaction formula 3) and (reaction formula 4)proceed spontaneously, while the reaction between the MgO barrier layer305 and the organic acid gas does not proceed spontaneously.

As a result, the first reaction proceeds on the surface oxide layer1301, and the volatile metal complexes and H₂O are produced. On theother hand, since the first reaction does not proceed on the MgO barrierlayer 305, H₂O is not produced. The metal complexes which are reactionproducts are preferably ones having a low volatilization temperaturefrom the viewpoint of removal by volatilization, but a volatile metalcomplex containing a carboxyl group or an aldehyde group may also beused. The volatilization temperature of the metal complex is preferablyequal to or lower than the temperature in the chamber.

After the first reaction, the second reaction is generated between H₂Oand the precursor gas. H₂O is the reaction product in the first reactiondescribed above. By the second reaction between H₂O and the precursorgas, the hard coating 1305 having high etching resistance is formed onthe upper surface and side walls of the hard mask 308 from which thesurface oxide layer 1301 shown in FIG. 13B is removed and on the sidewalls of the capping layer 307 and the free layer 306. When theprecursor gas is aluminum acetylacetone Al(acac)₃,

3H₂O+2Al(acac)₃=Al₂O₃+6H(acac)   (reaction formula 2)

similar to the first embodiment, Al₂O₃ is spontaneously producedaccording to (reaction formula 2). As the hard coating 1305, it isdesirable to use a material such as Al₂O₃ which is more excellent inetching resistance than Ta, has high insulation properties and does notexhibit magnetism.

When the organic acid gas and the precursor gas are simultaneouslyintroduced and H₂O produced in the first reaction remains after thesecond reaction, the deliquescent MgO barrier layer 305 may beinfluenced, causing problems such as short-circuit failure and magneticproperty deterioration. Therefore, the molar ratio of the introducedorganic acid gas to the precursor gas is adjusted such that H₂O does notremain after the second reaction.

For example, when the formic acid HCOOH which is a monovalent acid isused as the organic acid gas and aluminum acetylacetone Al(acac)₃ isused as the precursor gas, the molar ratio of produced H₂O is 3 withrespect to the molar ratio 6 of the formic acid according to (reactionformula 1), (reaction formula 3), and (reaction formula 4). At thistime, if the molar ratio of aluminum acetylacetone Al(acac)₃ is 2, allthe H₂O are consumed in (reaction formula 2). That is, if the molarratio of aluminum acetylacetone Al(acac)₃ is 1/3 or more with respect tothe molar ratio 1 of the formic acid, H₂O produced by the first reactioncan be removed by the second reaction. In general, when the organic acidgas is an n-valent acid and the valence of the metal elementcorresponding to the precursor gas is m, the precursor gas may have amolar ratio of n/m or more with respect to 1 mole of the organic acidgas.

In step 1203, as in the first embodiment, it is possible to use theorganic acids as exemplified in FIG. 4. However, a reaction (firstreaction) for producing a corresponding volatile metal complex from thesurface oxide layer 1301 spontaneously proceeds with respect to eachgas, and it is necessary to set a temperature and a pressure thatsatisfy a condition under which the reduction reaction or modificationof the MgO barrier layer 305 does not proceed.

Further, among the precursors shown in FIG. 5, the Al₂O₃ precursor andthe SiON precursor are effective as the precursor. A precursor isselected which satisfies the characteristics of the hard coating 1305,that is, more excellent in etching resistance than the hard mask 308,having high insulation properties and not exhibiting magnetism. In thiscase, the molar ratio of precursor/organic acid may be a molar ratio inconsideration of the valence of the metal element corresponding to theprecursor gas shown in FIG. 7 in which the organic acid gas is amonovalent acid.

In step 1204, as shown in FIG. 13C, the MgO barrier layer 305, the fixedlayer 304, and the underlayer 303 are etched. The etching is preferablyperformed by the plasma etching having a high etching selectivity, butmay also be performed by the ion beam etching. In this etching step, thestacked film composed of the MgO barrier layer 305, the fixed layer 304,and the underlayer 303 and having a total thickness of several tens ofnanometers is etched, but the upper surface and the side walls of thehard mask 308 are protected by the hard coating 1305, and as a result,the effect of preventing the corner rounding of the hard mask 308 isobtained. Accordingly, it is possible to prevent a reduction in the filmthickness of the hard mask 308 and to prevent a reduction in the processmargin of the step (step 1206) of exposing the hard mask 308 forelectrically connecting the magnetic tunnel junction with the upperelectrode film in subsequent steps.

In step 1205, as shown in FIG. 13D, a protective film 1306 covering themagnetic tunnel junction is formed. The protective film 1306 is formedby a plasma CVD method. Since the side walls of the free layer 306 arecovered with the hard coating 1305, it is possible to preventdeterioration of characteristics of the free layer 306 due to gases suchas hydrogen, nitrogen, and oxygen or plasma produced during plasma CVDfilm formation. As the protective film 1306, it is desirable to form aprotective film made of an insulating material such as SiN, SiO₂, Al₂O₃,Ta₂O₅, or TiO₂ because of excellent insulating properties thereof. Themethod of forming the protective film 1306 is not limited to the CVDmethod, and a sputtering method may be used.

Finally, in the step 1206, as shown in FIG. 13E, the insulatinginterlayer 313 is formed between the magnetic tunnel junctions, theprotective film 1306 covering the upper surface of the hard mask 308 andthe hard coating 1305 are removed, and the upper electrode film 314 isformed so as to be electrically connected to the hard mask 308.

In the cross-sectional structure of the magnetic tunnel junction of thepresent embodiment, a step 1307 is provided between the free layer 306and the MgO barrier layer 305, and the insulating hard coating 1305 isformed on the side walls of the free layer 306. That is, the diameter ofthe free layer 306 is smaller than the diameter of the MgO barrier layer305 or the fixed layer 304 by the thickness of the hard coating 1305.With this shape, it is possible to prevent the occurrence of ashort-circuit failure between the free layer and the fixed layer causedby the re-attachment of the metal material etched in step 1204 to thesidewalls of the free layer 306, the MgO barrier layer 305, and thefixed layer 304.

The stacked structure of the applicable magnetic tunnel junction of thepresent embodiment is not limited to the magnetic tunnel junction shownin FIG. 13E. For example, in order to stabilize the magnetizationdirection of the free layer, a two-layer MgO film as shown in FIG. 15Amay be used as a stacked structure in the magnetic tunnel junction. Alower electrode film 701, an underlayer 702, a fixed layer 703, and aMgO barrier layer 704 are the same as the corresponding layers 302 to305 in FIG. 13A. In the stacked structure shown in FIG. 15A, instead ofa single-layer free layer, a lower free layer 705 and an upper freelayer 707 separated by an insertion layer 706 made of a nonmagneticmetal material such as Ta, and a MgO capping layer 708 are stacked inthis order on the MgO barrier layer 704. A resist mask 710 having aprescribed pattern is formed on a hard mask 709 for element isolation.

In this case, when the MgO barrier layer 704 corresponding to the MgObarrier layer 305 in FIG. 13A is to be exposed, it is necessary to etchthe stacked free layers, and it is necessary to etch the stacked filmhaving a thickness of about 2 to 3 times that of the magnetic tunneljunction which has a single-layer free layer. Since the etching timeuntil the MgO barrier layer 704 is exposed is increased by 2 to 3 times,the corner rounding of the hard mask 709 proceeds in this period. Thus,in a case where the stacked structure of the magnetic tunnel junctionincludes a plurality of MgO layers, a partial stacked film stacked aboveany of the MgO layers may be etched first etching the barrier layer. Inthis case, it is possible to minimize the corner rounding of the hardmask by first etching the partial stacked film above the uppermost MgOlayer, such as the MgO capping layer 708.

A method of manufacturing the magnetic tunnel junction in this case isshown in FIG. 14 as a flowchart. In step 1401, as shown in FIG. 15A, thehard mask 709 is patterned. Subsequently, in step 1402, the uppersurface and the side walls of the hard mask 709 are oxidized by exposingthe magnetic tunnel junction to the oxidizing gas or the plasma usingthe oxidizing gas, so as to form a surface oxide layer 711 of Ta₂O₅ orthe like as shown in FIG. 15B. Subsequent steps 1403 to 1406 are thesame as steps 1203 to 1206 shown in FIG. 12, respectively. As a result,the magnetic tunnel junction shown in FIG. 15C is formed.

Fourth Embodiment

In a fourth embodiment, a case where plasma etching without using anoxidizing gas is applied or ion beam etching is applied when a stackedfilm is processed will be described. When these processes are applied, asurface oxide layer is not formed in a step (corresponding to step 1202in FIG. 12 or step 1402 in FIG. 14) of etching a hard mask or a freelayer of a magnetic tunnel junction. However, without the surface oxidelayer 1301 (711), the formation of the hard coating 1305 (712) by theintroduction of an organic acid and a precursor does not proceed.Therefore, in the present embodiment, even when a free layer isprocessed by the plasma etching using a gas containing no oxygen or bythe ion beam etching, the surface oxide layer is formed on side wallsand the upper surface of the hard mask by introducing an oxidation stepafter the etching.

FIG. 16 shows a process flow of a method of manufacturing the magnetictunnel junction according to the present embodiment. The manufacture ofthe magnetic tunnel junction shown in FIG. 13E is described as anexample, and the present embodiment is also applicable to themanufacture of the magnetic tunnel junction shown in FIG. 15C. Thedifferences between the present embodiment and the third embodiment liein step 1602 and step 1603.

Step 1602 is a step of etching the stacked film until the free layer bythe plasma etching without using the oxidizing gas or by the ion beametching. Since the gas containing no oxygen is used, a surface oxidelayer is not formed on the upper surface and the side walls of the hardmask 308 and on the side walls the capping layer 307 and the free layer306. In the plasma etching using the gas containing no oxygen, areactive gas such as hydrogen or nitrogen is used, and in the ion beametching, a rare gas such as He, Ne, Ar, Kr, or Xe or a mixed gas thereofis used.

Subsequently, the oxidation step is introduced after the etching (step1603). By introducing this step, the surface oxide layer 1301 same as inthe third embodiment can be formed on the upper surface and the sidewalls of the hard mask 308 and on the side walls of the capping layer307 and the free layer 306. Specifically, by exposing the magnetictunnel junction to the oxidizing gas or the plasma using the oxidizinggas, the upper surface and the side walls of the hard mask 308 and theside walls of the capping layer 307 and free layer 306 can be oxidized.The other steps 1601, 1604 to 1608 are the same as steps 1201, 1203 to1206 in FIG. 12.

Thus, in the present embodiment, when the plasma etching using the gascontaining no oxygen or the ion beam etching is used in the etching stepof the hard mask, the oxidation step is introduced after the etching. Asa result, by forming the surface oxide layer on the upper surface andthe side walls of the hard mask 308 and further forming the hard coatingfrom the surface oxide layer, corner rounding of the hard mask 308 canbe reduced.

Hereinafter, a modification applicable to the process flows of the thirdembodiment and the fourth embodiment will be described. In step 1203 inFIG. 12, step 1403 in FIG. 14, and step 1604 in FIG. 16, the organicacid gas and the film forming seed gas are introduced simultaneously. Asdescribed in the modification of the first embodiment or the secondembodiment, when the organic acid gas and the precursor gas areintroduced simultaneously, the organic acid gas and the precursor gasmay be directly reacted due to the combination thereof, and thecombination of the organic acid gas and the precursor gas that can beintroduced simultaneously is limited. In this case, it is also effectiveto alternately introduce the organic acid gas and the precursor gas toprevent the direct reaction between the organic acid gas and theprecursor gas.

FIG. 17 shows a process flow of a method of manufacturing a magnetictunnel junction according to the present modification. The presentmodification is also applicable to the manufacture of any of themagnetic tunnel junction shown in FIG. 13E and the magnetic tunneljunction shown in FIG. 15C. Step 1701 corresponds to step 1202 in FIG.12, step 1402 in FIG. 14, and steps 1602 to 1603 in FIG. 16. Step 1702shows a step of alternately repeating the step 1 of introducing theorganic acid gas and the step 2 of introducing the precursor gas. Thenumber of times of alternately introducing the organic acid gas andprecursor gas is one or more. Accordingly, a surface oxide layer isremoved, and a hard coating made of Al₂O₃ and the like is formed. On theother hand, the hard coating is not formed on the surface of the MgOlayer. Step 1703 corresponds to step 1204 in FIG. 12, step 1404 in FIG.14, and step 1605 in FIG. 16.

Another modification of the process flow of the method of manufacturingthe magnetic tunnel junction will be described. In the third embodiment,the fourth embodiment, or the modification thereof, when the hardcoating formed in the magnetic tunnel junction contains impurities suchas C, the insulation and etching resistance may decrease due to the hardcoating. Thus, a heat treatment is performed after the formation of thehard coating. Specifically, the heat treatment is applied to the hardcoating immediately after step 1203 in FIG. 12, step 1403 in FIG. 14, orstep 1604 in FIG. 16.

Therefore, the treatment time and the treatment temperature (150° C. to400° C.) under which the impurity reduction of the hard coating ispromoted are set, and the magnetic tunnel junction covered with the hardcoating is heated at 400° C. for minutes, for example. With this heatingstep, the impurities such as C can be reduced, and the insulationproperty of the hard coating can be enhanced. In addition, by reducingthe impurities, the crystallinity of the hard coating can be increased,and the etching resistance of the hard coating can be improved. When themagnetic tunnel junction is heated at a temperature higher than 400° C.,the magnetic properties may deteriorate, and therefore, this heatingstep is preferably performed at 400° C. or lower. As the heat treatmentmethod, a method of directly heating the substrate by a heater, heatingthe substrate by infrared light or laser light irradiation, heating thesubstrate by plasma, or the like can be applied.

In order to improve the insulating property and the etching resistanceof the hard coating 1305 (712), the heat treatment may be performed inan atmosphere using a reactive gas such as oxygen or nitrogen. When thereactive gas and the exposed MgO barrier layer 305 (the MgO cappinglayer 708) are reacted, the reaction product is limited to the surfaceof the MgO barrier layer 305 (MgO capping layer 708) and is then removedin the subsequent etching step, so that the characteristics of themagnetic tunnel junction are not influenced. Thus, by introducing theheat treatment after the hard coating 1305 is formed, the insulatingproperty and the etching resistance of the hard coating 1305 can beimproved.

The invention made by the present inventor is described above in detailbased on the embodiments, but the invention is not limited to the aboveembodiments, and various changes can be made within the scope notdeparting from the gist of the invention. In addition, the plurality ofillustrated configuration examples and modifications may be used incombination as long as no contradiction arises. For example, bycombining the first embodiment or the second embodiment with the thirdembodiment or the fourth embodiment, it is possible to protect themagnetic layer while suppressing the corner rounding of the hard mask.Also, the exemplified materials are merely examples, and other materialscompatible with the requirements shown in the embodiments maybe used.For example, although the example using MgO as the barrier layer of themagnetic tunnel junction has been shown, ZnO and Al₃O₃ can also be usedas the barrier layer. When the materials are used, conditions underwhich the barrier layer is not deteriorated can be relaxed compared tothe case of MgO, and for example, the pressure in the chamber can be setwithin a range of 0.1 Pa to 1e⁵ Pa, and the treatment temperaturethereof can be set within a range of 0 to 400° C. In addition, since thedeliquescent property with respect to H₂O is not shown, the molar ratioof the organic acid gas to the precursor gas can be set as desired.

REFERENCE SIGN LIST

-   101 Si substrate-   102 lower electrode film-   103 underlayer-   104 fixed layer-   105 MgO barrier layer-   106 free layer-   107 capping layer-   108 hard mask-   109 protective film-   110 magnetic oxide layer-   301 Si substrate-   302, 701 lower electrode film-   303, 702 underlayer-   304, 703 fixed layer-   305, 704 MgO barrier layer-   306 free layer-   307 capping layer-   308, 709 hard mask-   309, 710 resist mask-   310 magnetic oxide layer-   311 first protective film-   312 second protective film-   313, 714 insulating interlayer-   314, 715 upper electrode film-   705 lower free layer-   706 insertion layer-   707 upper free layer-   708 capping layer-   711, 1301 surface oxide layer-   712, 1305 hard coating-   713, 1306 protective film-   1307 step

1. A method of manufacturing a magnetic tunnel junction, comprising: afirst step of etching a stacked film including a first magnetic layer, aMgO barrier layer, and a second magnetic layer stacked in order byplasma etching using an oxidizing gas to form the magnetic tunneljunction; and a second step of simultaneously introducing an organicacid gas which is an n-valent acid and a precursor gas whose valence ofa corresponding metal element is m, to form a first protective film onside walls of the magnetic tunnel junction; wherein in the second step,the precursor gas is introduced at a molar ratio of n/m or more withrespect to 1 mole of the organic acid gas introduced.
 2. The method ofmanufacturing a magnetic tunnel junction according to claim 1, furthercomprising: a third step of forming, by a plasma CVD method, a secondprotective film on the magnetic tunnel junction on which the firstprotective film is formed.
 3. A method of manufacturing a magnetictunnel junction, comprising: a first step of etching a stacked filmincluding a first magnetic layer, a MgO barrier layer, and a secondmagnetic layer stacked in order by plasma etching without using anoxidizing gas or by ion beam etching to form the magnetic tunneljunction; an oxidation step of oxidizing side walls of the magnetictunnel junction; a second step of simultaneously introducing an organicacid gas which is an n-valent acid and a precursor gas whose valence ofa corresponding metal element is m, to form a first protective film onthe side walls of the magnetic tunnel junction; and a third step offorming, by a plasma CVD method, a second protective film on themagnetic tunnel junction on which the first protective film is formed,wherein in the second step, the precursor gas is introduced at a molarratio of n/m or more with respect to 1 mole of the organic acid gasintroduced.
 4. The method of manufacturing a magnetic tunnel junctionaccording to claim 1, wherein the second step includes a first reactionin which the organic acid gas reacts with a magnetic oxide layer formedon the side walls of the magnetic tunnel junction to produce a volatilemetal complex and H₂O, and the oxide magnetic layer is removed byvolatilization, and a second reaction in which the precursor gas reactswith H₂O to form, as the first protective film, an oxide filmcorresponding to the precursor gas on side walls of the first magneticlayer and the second magnetic layer.
 5. A method of manufacturing amagnetic tunnel junction, comprising: a first step of forming themagnetic tunnel junction in which a first magnetic layer, a MgO barrierlayer, and a second magnetic layer are stacked in order and a magneticoxide layer is formed on side walls of the first magnetic layer and thesecond magnetic layer; a second step of introducing an organic acid gaswhich is an n-valent acid, reacting the organic acid gas with themagnetic oxide layer to produce a volatile metal complex and H₂O, andremoving the magnetic oxide layer by volatilization; and a third step ofintroducing a precursor gas having a corresponding metal element valenceof m and reacting the precursor gas with H₂O to form an oxide filmcorresponding to the precursor gas as a first protective film, whereinthe second step and the third step are repeated.
 6. The method ofmanufacturing a magnetic tunnel junction according to claim 5, furthercomprising: a fourth step of forming, by a plasma CVD method, a secondprotective film on the magnetic tunnel junction on which the firstprotective film is formed.
 7. The method of manufacturing a magnetictunnel junction according to claim 2, wherein the second protective filmis formed after a heat treatment is performed on the first protectivefilm. 8-18. (canceled)